title: Superior segment facet joint violation and cortical violation after minimally invasive pedicle screw placement.
abstract: BACKGROUND
  Minimally invasive approaches to the lumbar spine allow for pedicle screw placement through a muscle-splitting paraspinal approach. These techniques are highly dependent on fluoroscopy and do not allow for direct visualization of anatomic landmarks. The effect of this on the accuracy of pedicle screw placement is not well described. The purpose of this study was to evaluate the rate of violation of the superior segment facet joint and rates of cortical violation after minimally invasive pedicle screw placement.
  
  
  OBJECTIVE
  To evaluate the rate of cortical violation and involvement of the superior segment facet after minimally invasive pedicle screw placement.
  
  
  METHODS
  Retrospective chart review.
  
  
  METHODS
  Patients who underwent minimally invasive pedicle screw placement by a single surgeon between January 2004 and July 2009.
  
  
  METHODS
  Violation of the superior segment facet joint or cortical violation identified on computed tomography (CT).
  
  
  METHODS
  This study consisted of a consecutive series of adult patients undergoing minimally invasive pedicle screw placement by a single surgeon for degenerative lumbar spinal conditions. Routine postoperative CT was obtained and evaluated for involvement of the superior segment facet joint and for cortical violation.
  
  
  RESULTS
  Sixty-one consecutive patients (282 pedicle screws) met the study criteria and were included in the study, including 42 single-level fusions and 19 two-level fusions. Seven cortical breaches were identified for a rate of 2.48%. Seven patients had involvement of the superior-level facet for an incidence of 11.48%. One patient required revision for a malpositioned pedicle screw.
  
  
  CONCLUSIONS
  This study revealed a low rate of superior segment facet violation and cortical violation after minimally invasive pedicle screw placement. This rate of superior-level facet involvement is significantly lower than previously reported after open procedures. The rate of cortical violation is similar to previous reports in the literature with a low revision rate.
authors.affiliation: Orthopaedic Surgery Service, Tripler Army Medical Center, 1 Jarrett White Rd, Honolulu, HI 96589, USA. Jeffrey.bruce.knox@us.army.mil
authors.forename: Jeffrey B
authors.initials: JB
authors.lastname: Knox
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Dai
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Orchowski
mesh_terms: D000328:Adult; D001863:Bone Screws / Q000009:adverse effects*; D005260:Female; D006801:Humans; D007431:Intraoperative Complications / Q000453:epidemiology / Q000209:etiology*; D008159:Lumbar Vertebrae / Q000293:injuries* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D019060:Minimally Invasive Surgical Procedures / Q000009:adverse effects* / Q000295:instrumentation; D011183:Postoperative Complications; D012086:Reoperation; D015203:Reproducibility of Results; D012189:Retrospective Studies; D013123:Spinal Fusion / Q000009:adverse effects* / Q000295:instrumentation; D014057:Tomography, X-Ray Computed; D055815:Young Adult; D021801:Zygapophyseal Joint / Q000293:injuries*